Integrated circuits have been increasingly made more highly large-scale-integrated, and a device having a capacity of 16 Mbits has been developed. Miniaturization and improvement in the switching speed of each electronic element of the integrated circuit has made remarkable progress. However, as progress has been made in making a device more highly-integrated, interconnections in the device have become highly dense and more complicated. Consequently, a stray capacity has been increased, and therefore a signal propagation speed has been limited accordingly. As a result, despite the high switching speed of the electronic devices, an actual operation speed of the integrated circuit is limited by the signal propagation speed. Accordingly, a so-called optical connection, in which light is used for signal transmission among electronic devices, has been proposed to overcome the above problem.
The optical connection is a connection of electric signals to be realized by using optical interconnection. In other words, electric interconnection is not used therein. In the optical interconnection, the signal propagation speed only depends on the refractive index and the line length, and is not affected by the capacitive impedance. In addition, little cross talk occurs in the lines, even if the lines are proximate to each other, because optical lines are non-inductive, so that no limitation occurs in connection density due to the non-existence of induction. Even more, it is possible to connect optical lines in intersecting pattern. When optical lines are spatially connected, complicated interconnection becomes unnecessary and two or three-dimensional interconnection (parallel connection) can be realized. Additionally, connection density is much increased by using wavelength multiplexing, etc.
Further, optical functional connecting systems have been proposed, in which highly developed signal processing can be realized by not merely using light for signal connection, but by adding optical processing function to the above optical connection. In order to realize optical signal processing systems, optical exchanging systems, etc. in addition to optical connection, devices which are sufficiently compact, consume a small amount of power, and have precisely designable and reproducible performance characteristics are required. For this purpose, a vertical to surface transmission electrophotonic device (abbreviated VSTEP hereinafter) having functions such as light emission, light receiving, memory, threshold, etc., as reported by Tashiro et al. on pp. 329-331, in "Appl. Phys. Lett. 54(4), Jan. 23, 1989" has been proposed. The VSTEP is a device having a pnpn structure which emits a light responsive to a small-power trigger light, when a predetermined voltage is applied thereto, and continues to emit light, even if the input of the trigger light is stopped. A conventional driving apparatus of this pnpn device will be explained later in detail.
However, the conventional driving apparatus for a pnpn device has the following disadvantages:
1. The operation speed thereof is limited to the switching speed of the device, since the light output is obtained by the switching operation of the device.
2. The light power of the input trigger light is relatively high, since it is also used for the switching operation.
3. Since the light output is controlled by the strength of the applied voltage and/or the input trigger light, the control operation of the light output is difficult.